1. Field of the Invention
The present invention relates to a surface plasmon resonance sensor chip utilizing a surface plasmon resonance phenomenon, and in particular, to a surface plasmon resonance sensor chip for use in a biological function analysis using in a vitro sample and in an environment measurement.
2. Description of the Background Art
Currently, in biochemical and medical fields, it is requested to find out a correlation between bioactive molecules in a biological body with high accuracy. Accordingly, there is a need for sensors capable of measuring progress of biochemical reaction of bioactive molecule or the like with high accuracy, and having a small size, and the research is advanced. Among such sensors, a method using a light for measurement is excellent in the aspect of sensitivity, and various techniques including a colorimetric method, a fluorescence method and a luminescence method have been developed. However, sensors using these techniques are bulky, and find a report that quenching phenomenon may occur due to color degradation of pigment. Also sensitivity in measurement by these techniques seems to be reaching a peak. Also many of sensors that are mainly used at present are so designed that the measurement is conducted in the condition that a measurement sample is dispersed in a solution, and according to such a design, a certain or longer optical path length is required. This makes it difficult to miniaturize the sensor.
In light of this, a sensor using such a sensing method that involves immobilizing a biological molecule on a substrate, and measuring reaction occurring on or near the substrate surface is recently proposed. In particular, sensors using a surface plasmon resonance spectroscopy attract attention because of excellent sensitivity and possibility of miniaturization (see, for example, K. Kurihara et al., Anal. Chem. 74(3): 696-701 (2002) (Non-Patent Document 1) and Shumaker-Parry J S et al., Anal. Chem. 76 (4):918-929 (2004) (Non-Patent Document 2)).
FIG. 3 is a schematic perspective view of one exemplary embodiment of a sensor utilizing a surface plasmon resonance phenomenon.
In the following, description will be made based on FIG. 3. A sensor shown in FIG. 3 includes a light source 80, a prism 81, a dielectric substrate 82, and a metal film 84, and dielectric substrate 82 is covered with metal film 84, and an antibody 85 serving as a receptor is immobilized on a surface of metal film 84. And it is possible to measure the quantity of a target molecule 86 that specifically binds to antibody 85 in a measurement sample.
First, an incident light λ1 is caused to enter dielectric substrate 82 covered with metal film 84, from light source 80 through prism 81. Incident light λ1 passes through dielectric substrate 82 and is then reflected at metal film 84, and an outgoing light λ2 arises through prism 81. At this time, when incident light λ1 and outgoing light λ2 are set at a certain incident angle and at a certain reflection angle, a surface plasmon resonance is observed in a boundary face between metal film 84 and dielectric substrate 82. And when target molecule 86 binds to immobilized antibody 85 in the condition that incident light λ1 and outgoing light λ2 are set so that the surface plasmon resonance is observed, the surface plasmon resonance will change (see, for example, Japanese Patent Laying-Open No. 2003-279476 (Patent Document 1) and Japanese Patent Laying-Open No. 2003-042944 (Patent Document 2)).
However, in conventional surface plasmon resonance sensors, it is necessary to arrange a chip and an optical system so that certain incident and reflection angles are provided for enabling entry of incident light λ1 through prism 81 or a transparent substrate of quartz or the like. This makes significant miniaturization difficult. It is known in principle that a loss arises in efficiency of occurrence of the surface plasmon resonance because incident light λ1 transmits to dielectric substrate 82 covered with metal film 84 through prism 81 or the like.
FIG. 4 is a schematic perspective view of one exemplary embodiment of a sensor utilizing a transmission-type surface plasmon resonance. FIG. 5 is a schematic section view showing a cross-section of the sensor in FIG. 4. FIG. 6 is a schematic section view showing a cross-section as another form of the sensor in FIG. 4.
In the following, description will be made based on FIGS. 4 to 6. In order to alleviate the problem as described above, the sensor as shown in FIG. 4 and FIG. 5 has been proposed at present. The sensor shown in FIG. 4 includes a chip 100 and a laser 60 serving as a light source. Chip 100 has a first dielectric layer 52, a metal layer 54 disposed on first dielectric layer 52, and a second dielectric layer 53 covering metal layer 54. Chip 100 is provided on a substrate 51. Chip 100 is provided with an opening for making a part of a surface on the side of second dielectric layer 53 of metal layer 54 be exposed and allowing a measurement sample and the surface to contact each other. Metal layer 54 at the opening is immobilized with an antibody 55 serving as a biological molecule which is to react with a target molecule contained in a measurement sample. Laser 60 emits a laser light 61 and laser light 61 enters from one end of metal layer 54 horizontally with respect to metal layer 54. Laser light 61 travels in the longitudinal direction of metal layer 54 serving as a waveguide, and outgoes from the other end through metal layer 54. Then an outgoing light 71 outgoing from the other end is detected.
According to this surface plasmon resonance sensor, it is possible to resolve arranging an angle between a chip and a light source, and to alleviate a light transmission loss at the prism.
Here, the surface plasmon resonance sensor as shown in FIG. 4 requires such a structure that a metal layer is sandwiched between dielectric members. In such a structure, relationship in a refractive index and adhesion between the dielectric member and the metal layer greatly influence on a performance of the surface plasmon resonance sensor. The surface plasmon resonance sensor as shown in FIG. 4 and FIG. 5 faces the problem that a transmission loss arises due to poor adhesion between the metal layer and the dielectric member, resulting in reduction in sensitivity in measurement. As a method of improving the adhesion, there is known a surface plasmon resonance sensor as shown in FIG. 6 in which different kind of metal 57 is sandwiched between the metal layer and the dielectric member as shown in FIG. 5, however, it is proved that a transmission loss arises due to a transmission-type surface plasmon resonance absorption by different kind of metal 57, and sensitivity of the surface plasmon resonance sensor is deteriorated accordingly.
At present, a surface plasmon resonance sensor for use as a biosensor is also proposed (Japanese Patent Laying-Open No. 2006-250668 (see Patent Document 3)).